'\"macro stdmacro
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.TH PMDAMMV 1 "PCP" "Performance Co-Pilot"
.SH NAME
\f3pmdammv\f1 \- memory mapped values performance metrics domain agent (PMDA)
.SH SYNOPSIS
\f3$PCP_PMDAS_DIR/mmv/pmdammv\f1
[\f3\-d\f1 \f2domain\f1]
[\f3\-l\f1 \f2logfile\f1]
[\f3\-U\f1 \f2username\f1]
.SH DESCRIPTION
.B pmdammv
is a Performance Metrics Domain Agent (PMDA) which exports
application level performance metrics using memory mapped files.
It offers an extremely low overhead instrumentation facility
that is well-suited to long running, mission critical applications
where it is desirable to have performance metrics and availability
information permanently enabled.
.PP
The
.B mmv
PMDA exports instrumentation that has been added to an application
using the MMV APIs (refer to
.BR mmv_stats_init (3)
and
.BR mmv (5)
for further details).
These APIs can be called from several languages, including C, C++,
Perl, Python, Java (via the separate ``Parfait'' class library) and
GoLang (via the separate ``Speed'' library).
.PP
A brief description of the
.B pmdammv
command line options follows:
.TP 5
.B \-d
It is absolutely crucial that the performance metrics
.I domain
number specified here is unique and consistent.
That is,
.I domain
should be different for every PMDA on the one host, and the same
.I domain
number should be used for the same PMDA on all hosts.
.TP
.B \-l
Location of the log file.  By default, a log file named
.I mmv.log
is written in the current directory of
.BR pmcd (1)
when
.B pmdammv
is started, i.e.
.BR $PCP_LOG_DIR/pmcd .
If the log file cannot
be created or is not writable, output is written to the standard error instead.
.TP
.B \-U
User account under which to run the agent.
The default is the unprivileged "pcp" account in current versions of PCP,
but in older versions the superuser account ("root") was used by default.
.SH INSTALLATION
Firstly, a security model for interprocess communication between
instrumented applications and
.B pmdammv
(running as a shared library inside
.BR pmcd )
must be chosen and established.
.PP
This communication occurs through memory mapped files in a
location known to both
.B pmdammv
and the instrumented applications.
That location is
.IR $PCP_TMP_DIR/mmv ,
although that is often hidden behind application APIs such as ``Parfait''
and
.BR mmv_stats_init (3).
The permissions set on this directory indicate the security model in use.
.PP
The more secure method is to use an existing unprivileged group which
is shared by instrumented applications,
.B pmcd
and
.B pmdammv
such as the "pcp" group.
.PP
.ft CW
.nf
.in +0.5i
# . /etc/pcp.env
# mkdir -m 775 $PCP_TMP_DIR/mmv
# chgrp pcp $PCP_TMP_DIR/mmv
.in
.fi
.ft 1
.PP
Since this method requires instrumented applications to use this
non-default group (see
.BR newgrp (1)
and
.BR setgid (2))
a common alternative involves the use of a world-writeable
.I $PCP_TMP_DIR/mmv
directory with the sticky-bit set (similar to
.I /tmp
and
.IR /var/tmp ,
for example).
.PP
This allows any application, running under any user account,
to communicate with the PMDA (which runs under the "pcp" account
by default).
This may not be desirable for all environments and one should consider
the security implications of any directory setup like this (similar
classes of issues exist as those that affect the system temporary file
directories).
.PP
.B pmdammv
is enabled by default on all modern PCP installations, and thus
the names, help text and values for the mmv performance metrics are
available without the usual PMDA ./Install process.
.PP
If the
.I $PCP_TMP_DIR/mmv
directory does not exist, then the ./Install script can be used to
create a world-writeable sticky-bit-set directory for communication.
This is for backwards compatibility, as well as ease of use \- to use
this mechanism, do the following as root:
.PP
.ft CW
.nf
.in +0.5i
# rmdir $PCP_TMP_DIR/mmv
# cd $PCP_PMDAS_DIR/mmv
# ./Install
.in
.fi
.ft 1
.PP
This installation process will not overwrite any existing
.I $PCP_TMP_DIR/mmv
directory.
.PP
If you want to undo the installation, do the following as root:
.PP
.ft CW
.nf
.in +0.5i
# cd $PCP_PMDAS_DIR/mmv
# ./Remove
.in
.fi
.ft 1
.PP
.B pmdammv
is launched by
.BR pmcd
and should never be executed directly.
The Install and Remove scripts notify
.BR pmcd
when the agent is installed or removed.
.SH FILES
.PD 0
.TP 10
.B $PCP_PMCDCONF_PATH
command line options used to launch
.B pmdammv
.TP 10
.B $PCP_TMP_DIR/mmv
directory housing memory mapped value files
.TP 10
.B $PCP_PMDAS_DIR/mmv/help
default help text file for the mmv metrics
.TP 10
.B $PCP_PMDAS_DIR/mmv/Install
installation script for the
.B pmdammv
agent
.TP 10
.B $PCP_PMDAS_DIR/mmv/Remove
undo installation script for the
.B pmdammv
agent
.TP 10
.B $PCP_LOG_DIR/pmcd/mmv.log
default log file for error messages and other information from
.B pmdammv
.PD
.SH "PCP ENVIRONMENT"
Environment variables with the prefix
.B PCP_
are used to parameterize the file and directory names
used by PCP.
On each installation, the file
.I /etc/pcp.conf
contains the local values for these variables.
The
.B $PCP_CONF
variable may be used to specify an alternative
configuration file,
as described in
.BR pcp.conf (5).
.SH SEE ALSO
.BR PCPIntro (1),
.BR pmcd (1),
.BR newgrp (1),
.BR setgid (2),
.BR mmv_stats_init (3),
.BR mmv (5),
.BR pcp.conf (5)
and
.BR pcp.env (5).
